Flash memory may be a non-volatile memory medium having electrical data incapable of being erased although the flash memory is powered off. For semiconductor devices having high integration, a small-sized flash memory may be obtained. The floating gate (FG) of such a small-sized flash memory, in turn, may have a simple structure. Particularly, for semiconductor devices of 100 nm or less, the simplification of a floating gate is important since channel width is reduced.
Flash memory can be advantageous for exhibiting high data processing such as recording, reading, and erasing. Accordingly, flash memory is suitable for applications for basic I/O system (BIOS) for personal computer (PC) and data storage for a desk top box, a printer, a network server, and the like. Flash memory is also suitable for digital cameras, portable phones, and the like.
Flash memory has certain disadvantages such as high operational voltage of about 9V to 12V. It can be difficult to reduce the operational voltage without a reduction in other functions and without reducing reliability. Moreover, fabricating a flash memory that can be driven at low voltages of 5V or less using an oxide-nitride-oxide (ONO) structure can be difficult.
Such low operational voltages may be achieved through the use of flash memory fabrication processes involving nano-dot or nano-crystal structures. The density of nano-dot structures leads to differences in information storage capability of flash memory and thus, great density is desirable. However, small gaps between nano-dots may cause increases in leakage current and also a reduction in maintenance time. Accordingly, controlling the gap between nano-dots is important to fabricating a flash memory having a low operational voltage.